U.S. patent application number 13/258979 was filed with the patent office on 2012-01-19 for flameproof rayon fiber, method for manufacturing the same and flameproof fiber structure.
This patent application is currently assigned to DAIWABO RAYON CO., LTD.. Invention is credited to Shigeo Fushitani, Makoto Hayashi.
Application Number | 20120015185 13/258979 |
Document ID | / |
Family ID | 44226261 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120015185 |
Kind Code |
A1 |
Fushitani; Shigeo ; et
al. |
January 19, 2012 |
FLAMEPROOF RAYON FIBER, METHOD FOR MANUFACTURING THE SAME AND
FLAMEPROOF FIBER STRUCTURE
Abstract
A flameproof rayon fiber having excellent flameproofness as well
as excellent flame retardance, a method for manufacturing the same,
and a flameproof fiber structure are provided. The flameproof rayon
fiber according to the present invention includes components of
silicon and sodium. Glass remains when the fiber is burned at
800.degree. C., the glass component has a property of softening at
800.degree. C., and when subjected to an X-ray fluorescence
analysis, the rayon fiber has a silicon content in the range of 5
to 30% by mass and a sodium content in the range of 0.1 to 3% by
mass. The flameproof rayon fiber according to the present invention
can be manufactured by preparing an undiluted viscose solution;
adding a solution containing a silicate compound containing an
alkali metal to the undiluted viscose solution so as to make an
alkali metal-containing silicate compound-added viscose solution;
performing spurning by extruding the alkali metal-containing
silicate compound-added viscose solution through a spinneret into a
spinbath containing sulfuric acid, thus producing a fiber to be
treated containing the silicate compound; and treating, in a
scouring or aftertreatment process, the fiber to be treated with a
solution having a pH in the range of 4 to 11 and a buffer action
and containing sodium. A flameproof fiber structure of the present
invention contains at least 30% by mass of the flameproof rayon
fiber.
Inventors: |
Fushitani; Shigeo; (Shimane,
JP) ; Hayashi; Makoto; (Shimane, JP) |
Assignee: |
DAIWABO RAYON CO., LTD.
Osaka-shi, Osaka
JP
DAIWABO HOLDINGS CO., LTD.
Osaka-shi, Osaka
JP
|
Family ID: |
44226261 |
Appl. No.: |
13/258979 |
Filed: |
December 28, 2009 |
PCT Filed: |
December 28, 2009 |
PCT NO: |
PCT/JP2009/071771 |
371 Date: |
September 22, 2011 |
Current U.S.
Class: |
428/364 ;
264/183 |
Current CPC
Class: |
Y10T 428/2913 20150115;
D01F 2/10 20130101 |
Class at
Publication: |
428/364 ;
264/183 |
International
Class: |
D02G 3/00 20060101
D02G003/00; D01F 2/02 20060101 D01F002/02; D01F 8/02 20060101
D01F008/02 |
Claims
1. A flameproof rayon fiber having flameproofness, comprising:
components of silicon and sodium; wherein glass remains in the
rayon fiber when the rayon fiber is burned at 800.degree. C., the
glass has a property of softening at 800.degree. C., and when
subjected to an X-ray fluorescence analysis, the rayon fiber has a
silicon content in a range of 5 to 30% by mass and a sodium content
in a range of 0.1 to 3% by mass.
2. The flameproof rayon fiber according to claim 1, wherein the
rayon fiber has an LOI value of 31 or more by twisted fiber string
measurement (E-1) or an LOI value of 24 or more by nonwoven fabric
measurement (E-2) in conformity with JIS L 1091 E (oxygen index
test).
3. The flameproof rayon fiber according to claim 1, wherein the
rayon fiber has an ash content in a range of 10 to 50% by mass.
4. The flameproof rayon fiber according to claim 1, wherein the
ratio of the silicon content to the sodium content (mass ratio of
silicon/sodium) in the rayon fiber is in a range of 10 or more and
less than 90.
5. A method for manufacturing a flameproof rayon fiber, comprising:
preparing an undiluted viscose solution; adding a solution
containing a silicate compound containing an alkali metal to the
undiluted viscose solution so as to make an alkali metal-containing
silicate compound-added viscose solution; performing spinning by
extruding the silicate compound-added viscose solution through a
spinneret into a spinbath containing a sulfuric acid, thus
producing a fiber to be treated containing the silicate compound;
and treating, in a scouring or aftertreatment process, the fiber to
be treated with a solution having a pH in a range of 4 to 11 and a
buffer action and containing sodium.
6. A flameproof fiber structure comprising at least 30% by mass of
the flameproof rayon fiber according to claim 1.
7. The flameproof rayon fiber according to claim 2, wherein the
rayon fiber has an ash content in a range of 10 to 50% by mass.
8. The flameproof rayon fiber according to claim 2, wherein the
ratio of the silicon content to the sodium content (mass ratio of
silicon/sodium) in the rayon fiber is in a range of 10 or more and
less than 90.
9. The flameproof rayon fiber according to claim 3, wherein the
ratio of the silicon content to the sodium content (mass ratio of
silicon/sodium) in the rayon fiber is in a range of 10 or more and
less than 90.
10. The flameproof rayon fiber according to claim 7, wherein the
ratio of the silicon content to the sodium content (mass ratio of
silicon/sodium) in the rayon fiber is in a range of 10 or more and
less than 90.
11. The flameproof fiber structure according to claim 6, wherein
the rayon fiber has an LOI value of 31 or more by twisted fiber
string measurement (E-1) or an LOI value of 24 or more by nonwoven
fabric measurement (E-2) in conformity with JIS L 1091 E (oxygen
index test).
12. The flameproof fiber structure according to claim 6, wherein
the rayon fiber has an ash content in a range of 10 to 50% by
mass.
13. The flameproof fiber structure according to claim 11, wherein
the rayon fiber has an ash content in a range of 10 to 50% by
mass.
14. The flameproof fiber structure according to claim 6, wherein
the ratio of the silicon content to the sodium content (mass ratio
of silicon/sodium) in the rayon fiber is in a range of 10 or more
and less than 90.
15. The flameproof fiber structure according to claim 11, wherein
the ratio of the silicon content to the sodium content (mass ratio
of silicon/sodium) in the rayon fiber is in a range of 10 or more
and less than 90.
16. The flameproof fiber structure according to claim 12, wherein
the ratio of the silicon content to the sodium content (mass ratio
of silicon/sodium) in the rayon fiber is in a range of 10 or more
and less than 90.
17. The flameproof fiber structure according to claim 13, wherein
the ratio of the silicon content to the sodium content (mass ratio
of silicon/sodium) in the rayon fiber is in a range of 10 or more
and less than 90.
Description
TECHNICAL FIELD
[0001] The present invention relates to a flameproof rayon fiber, a
method for manufacturing the flameproof rayon fiber, and a
flameproof fiber structure.
BACKGROUND ART
[0002] Conventionally, for cellulose fibers having flame retardance
and manufacturing methods thereof a number of studies have been
conducted to improve flame retardance by facilitation of
carbonization. Recently, several techniques utilizing the following
have been proposed for flameproof cellulose fibers. By combining
cellulose and glass with the use of a viscose rayon spinning
technique, the glass remains even if the cellulose is decomposed,
so that burning stops. For example, Patent document 1 proposes
production of a composite fiber by mixing viscose and sodium
silicate and spinning the mixture in a bath containing sulfuric
acid. Patent document 2 proposes a cellulose fiber including
aluminum, which is obtained by mixing sodium silicate with viscose
and using sodium aluminate in the scouring process. Patent document
3 proposes a cellulose fiber including Mg, which is obtained by
mixing sodium silicate with viscose and bring the fiber into
contact with an alkali solution containing Mg in the scouring or
aftertreatment process.
[0003] However, the cellulose fiber disclosed in Patent document 1
merely is a complex of cellulose and silicic acid. Thus, when the
fiber is exposed to high temperatures, a glass skeleton is formed
but decomposition of cellulose cannot be inhibited. Therefore, it
is necessary to further improve the flame retardance. Further,
although the cellulose fiber disclosed in Patent document 2
contains aluminum, it has been suggested that aluminum could be
neurotoxic. Thus, a further improvement in safety is necessary.
Further, when the cellulose fiber disclosed in Patent document 3 is
exposed to high temperatures, a glass skeleton is formed, so that
not only the fiber exhibits a flameproof ability but also it has
washing durability. However, in the case of the flameproof rayon of
Patent document 3, efforts to perform Mg treatment may become
complicated.
PRIOR ART DOCUMENT
Patent Document
[0004] Patent document 1: British Patent No. 1,064,271 [0005]
Patent document 2: Japanese Patent No. 3179104 [0006] Patent
document 3: Japanese Patent No. 4094052
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0007] With the foregoing in mind, the present invention provides a
flameproof rayon fiber having excellent flameproofness as well as
excellent flame retardance, a method for manufacturing the
flameproof rayon fiber and a flameproof fiber structure.
Means for Solving Problem
[0008] The flameproof rayon fiber according to the present
invention is a rayon fiber that includes components of silicon and
sodium. Glass remains in the rayon fiber when the rayon fiber is
burned at 800.degree. C., the glass has the property of softening
at 800.degree. C., and when subjected to an X-ray fluorescence
analysis, the rayon fiber has a silicon content in the range of 5
to 30% by mass and a sodium content in a range of 0.1 to 3% by
mass.
[0009] The method for manufacturing the flameproof rayon fiber
according to the present invention includes preparing an undiluted
viscose solution; adding a solution containing a silicic compound
containing an alkali metal to the undiluted viscose solution so as
to make an alkali metal-containing silicic compound-added viscose
solution; performing spinning by extruding the silicic
compound-added viscose solution through a spinneret into a spinbath
containing a sulfuric acid, thus producing a fiber to be treated
containing the silicic compound; and treating, in a scouring or
aftertreatment process, the fiber to be treated with a solution
having a pH in the range of 4 to 11 and a buffer action and
containing sodium.
[0010] The flameproof fiber structure of the present invention
contains at least 30% by mass of the flameproof rayon fiber.
Effects of the Invention
[0011] The flameproof rayon fiber according to the present
invention exhibits excellent flameproof ability and self
extinguishability (flame retardance) because the rayon fiber
contains components of silicon and sodium. Further, the flameproof
rayon fiber according to the present invention is not halogenic.
Thus, even if the fiber is burned, gas that emerges due to the
burning does not contain toxic substances such as cyan and halogen
compounds. Moreover, since the principal component of the
flameproof rayon fiber according to the present invention is rayon,
the fiber is degradable in soil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a micrograph showing a flameproof rayon fiber of
one example of the present invention being ashed at 800.degree.
C.
[0013] FIG. 2 is a micrograph showing a flameproof rayon fiber of
another example of the present invention being ashed at 800.degree.
C.
[0014] FIG. 3 is a micrograph showing a flameproof rayon fiber of a
comparative example being ashed at 800.degree. C.
[0015] FIG. 4 is a micrograph showing a flameproof rayon fiber of
another comparative example being ashed at 800.degree. C.
DESCRIPTION OF THE INVENTION
[0016] In the present invention, flameproofness refers to a flame
barrier property that can be achieved as a result of a glass
skeleton being remaining. More specifically, even when in contact
with a flame, an afterflame time is short and a damaged area is
small. Such an ability is useful for providing a property in which,
for example, even when a cigarette smoked in bed falls onto a
sheet, the sheet only becomes charred and the fire does not spread.
Further, flame retardance refers to a property of having
self-extinguishability and a fiber itself is resistant to burning.
More specifically, it is such a property that even when fire is set
to an opened fiber staple, the fire self extinguishes without
causing a flash.
[0017] The flameproof rayon fiber according to the present
invention contains components of silicon and sodium. The rayon
fiber according to the present invention softens at temperatures
lower than 1000.degree. C., for example, at a temperature of about
800.degree. C. as the temperature of a burning cigarette, and has
biodegradability. Since components other than the rayon component
form compounds containing silicon and sodium (mainly, sodium
silicate), the rayon fiber has a reduced load to the
environment.
[0018] The rayon fiber is a fiber obtained by xanthating cellulose,
followed by dilution and dissolution in dilute alkali so as to
prepare viscose, and then coagulating and regenerating this
viscose. The rayon fiber is not limited particularly by its
material such as cellulose or manufacturing method.
[0019] Since the flameproof rayon fiber contains silicon and
sodium, it is assumed that the flameproof rayon fiber forms a soda
glass structure when it is burned and its softening point drops.
Consequently, the glass softens quickly in high temperatures such
as about 800.degree. C., inhibiting decomposition of cellulose.
Normally, when cellulose is burned, the burning continues because
gas resulting from the decomposition due to the heat is
combustible. However, because the flameproof rayon fiber forms a
soda glass structure when it is burned, decomposition of cellulose
is inhibited to suppress the burning and the fire self
extinguishes.
[0020] When subjected to an X-ray fluorescence analysis, the
flameproof rayon fiber has a silicon content of 5 to 30% by mass,
preferably in the range of 8 to 23% by mass, and more preferably in
the range of 13 to 19% by mass. By setting the silicon content of
the rayon fiber according to the present invention to the mentioned
range, it is possible to maintain the strength and texture of the
rayon fiber.
[0021] When subjected to an X-ray fluorescence analysis, the
flameproof rayon fiber has a sodium content of 0.1 to 3% by mass,
preferably in the range of 0.15 to 1.5% by mass, and more
preferably in the range of 0.2 to 1.0% by mass. By setting the
sodium content in the flameproof rayon fiber according to the
present invention to the mentioned range, it is possible to achieve
a flameproof rayon fiber having more favorable flameproofness and
self-extinguishability.
[0022] Further, when subjected to an X-ray fluorescence analysis,
the ratio of the silicon content to the sodium content (mass ratio
of silicon/sodium) in the flameproof rayon fiber is preferably 10
or more and less than 90. The mass ratio of silicon/sodium is a
parameter that indicates the susceptibility of the fiber to
softening. The smaller the mass ratio of silicon/sodium, the
likelier it is for the flameproof rayon fiber to soften when being
burned due to the formation of soda glass within the fiber, and
thus, the self-extinguishability (flame retardance) improves. The
mass ratio of silicon/sodium is more preferably 15 to 70. When the
mass ratio of silicon/sodium is less than 90, the chance of sodium
silicate (xNa.sub.2.ySiO.sub.2.zH.sub.2O; where x is 1 to 5,
y.gtoreq.x, and z is 1 to 3) being formed is relatively high, so
that favorable flame retardance can be achieved. Further, when the
mass ratio of silicon/sodium is 10 or more, the flameproof rayon
fiber softens while leaving a glass skeleton, so that favorable
flameproofness and flame retardance can be achieved.
[0023] Sodium may be present in the flameproof rayon fiber such
that at least part thereof is contained in the rayon fiber and the
remaining part is adhered to the surface of the rayon fiber.
Whether sodium is present in the rayon fiber (inside the fiber) or
not can be determined by washing the fiber with water. The silicon
and the sodium compound are not limited particularly by which state
they are in. They may be mixed uniformly in the fiber or may be
present in a compatible or incompatible state. As long as the
sodium is partially present in the form of a sodium compound such
as sodium silicate, the remaining may be contained in the form of
sodium salt such as sodium oxide and sodium hydroxide.
[0024] The flameproof rayon fiber has an ash content preferably in
the range of 10 to 50% by mass, more preferably in the range of 15
to 40% by mass, and particularly preferably in the range of 25 to
38% by mass. Here, the ash content refers to an inorganic material
left as a remainder after an organic material is incinerated at
high temperatures. When the ash content is less than 10% by mass,
the flameproofness of the flameproof rayon fiber tends to drop. In
contrast, when the ash content exceeds 50% by mass, the strength of
the flameproof rayon fiber tends to drop or the texture thereof
tends to be impaired. Further, when the ash content exceeds 40% by
mass, it tends to be difficult to achieve the same texture as
conventional rayon fibers that do not use a flame retardant.
Therefore, by setting the ash content of the flameproof rayon fiber
according to the present invention to the mentioned range, it is
possible to achieve a flameproof rayon fiber having favorable
flameproofness and favorable texture. In the present invention, the
ash content of the flameproof rayon fiber is measured in conformity
with JIS L 1015 8.20 and is a value expressed by percent by mass of
the mass of a component remaining after burning a flameproof rayon
fiber at 850.degree. C. with respect to an absolute dry mass of the
flameproof rayon fiber. The same holds true for the following.
[0025] The flameproof rayon fiber has an LOI value of preferably 31
or more, and more preferably 32 or more by twisted fiber string
measurement (E-1) in conformity with JIS L 1091 E (oxygen index
test). Further, the flameproof rayon fiber has an LOI value of
preferably 23 or more, and more preferably 24 or more by nonwoven
fabric measurement (E-2) in conformity with JIS L 1091 E (oxygen
index test). The LOI values of the rayon fiber according to the
present invention satisfy the mentioned ranges, respectively. Thus,
the flameproof rayon fiber is preferable because it has flame
retardance as well as flameproofness.
[0026] The flameproof rayon fiber has an L value (whiteness) of
preferably 40 to 90, more preferably 44 to 86, and particularly
preferably 48 to 70. The L value is a whiteness indicator with a
scale of 0 (black) to 100 (white). As the value is larger and
positive, the color becomes whiter. Although the L value of 100
means that the color is white, the whiteness of typical rayon
fibers is about 92 to 95. Due to a change in the hue of cellulose
at the time of heating, the color does not become pure white.
Therefore, it tends to be difficult to produce rayon fibers having
an L value of more than 90. As for rayon fibers having an L value
of less than 40, their hue tends to deteriorate when they are
processed in the form of product, so that the product value tends
to drop.
[0027] The flameproof rayon fiber is not particularly limited by
its fineness and generally has a fineness in the range of 1 to 17
dtex, and preferably in the range of 1.7 to 10 dtex. When the
fineness is less than 1 dtex, the strength of the rayon fiber tends
to drop. When the fineness exceeds 17 dtex, the thickness of the
fiber becomes excessively large, so that the fiber tends to be
coarse. Also, the flameproof rayon fiber is not particularly
limited by its length, either, and can be used as a filament or a
staple. The fiber length can be set freely, and the fiber with a
length of 5 to 20 mm can be used as a paper screen, a wallpaper or
the like and that with a length of 20 to 200 mm can be used for a
nonwoven fabric or a spun yarn. A filament tow can be used without
cutting after the scouring.
[0028] The cross-section of the flameproof rayon fiber is not
particularly limited by its shape but can be selected suitably
according to the intended use. For example, a circular shape, a
deformed circular shape, a hollow shape, an oblate shape, etc. can
be selected.
[0029] The flameproof rayon fiber according to the present
invention has useful physical properties that rayon as regenerated
cellulose generally has, such as biodegradability, water
absorptivity, hygroscopicity, antistatic property and thermal
stability. Since rayon as the principal component of the flameproof
rayon fiber according to the present invention has
biodegradability, it can be decomposed within one to three months
when buried in the soil. Further, the components other than rayon
are compounds principally containing silicic acid and sodium
(mainly, sodium silicate). Therefore, the flameproof rayon fiber
according to the present invention has a reduced load to the
environment.
[0030] The flameproof rayon fiber according to the present
invention can be obtained as follows. First, a silicic compound
containing an alkali metal, for example, sodium silicate
(Na.sub.2O.nSiO.sub.2.xH.sub.2O; where n is 1 to 3 and x is 10 to
20) is added to an undiluted viscose solution to prepare an alkali
metal-containing silicic compound-added viscose solution
(hereinafter, simply referred to as the viscose solution). Then,
spinning is carried out by extruding the viscose solution through a
spinneret into a spinbath containing a sulfuric acid
(H.sub.2SO.sub.4) to produce a fiber to be treated containing the
silicic compound. During the spinning process, the silicic compound
containing an alkali metal, for example, sodium silicate
(Na.sub.2O.nSiO.sub.2.xH.sub.2O; where n is 1 to 3 and x is 10 to
20) in the viscose solution reacts with the sulfuric acid
(H.sub.2SO.sub.4) and turns into silicon dioxide (SiO.sub.2; in the
form of polymer). Subsequently, in a scouring or aftertreatment
process, the obtained fiber is treated with a solution having a pH
in the range of 4 to 11 and a buffer action and containing sodium,
thus obtaining the flameproof rayon fiber according to the present
invention. As a result of this treatment, silicon and sodium react
with each other and form a compound. It is estimated that the
compound containing silicon and sodium has the following structure
in the rayon fiber. In the rayon fiber, silicic acid forms a
layered structure and sodium in the form of sodium oxide is present
between the layers of the unit structure. The silicic acid and the
sodium oxide are bonded to each other due to sharing some part of
oxygen, so that a gel of silicic acid and sodium is produced to
form sodium silicate (xNa.sub.2O.ySiO.sub.2.zH.sub.2O; where x is 1
to 5, y.gtoreq.x, and z is 1 to 3). On the other hand, conventional
flameproof rayon fiber manufacturing is carried out in the same
manner as the manufacturing method according to the present
invention until the step where sodium silicate reacts with sulfuric
acid and turns into silicon dioxide. However, since large sulfur
content will remain if nothing is done, the sulfur content has to
be removed through a scouring process. Since sodium remaining in
the fiber is also removed from the system during the scouring
process, sodium and silicic acid are not bonded to each other in
the fiber.
[0031] The spinbath can be a general acid spinbath containing
sulfuric acid, for example, a Muller bath containing
H.sub.2SO.sub.4, ZnSO.sub.4 and Na.sub.2SO.sub.4 in the ranges of
110 to 170 g/liter, 10 to 30 g/liter and 150 to 350 g/liter,
respectively. Further, the temperature of the spinbath generally is
45 to 65.degree. C.
[0032] The undiluted viscose solution may have a general
composition. For example, it is possible to use an undiluted
viscose solution containing cellulose, NaOH and CS.sub.2 in the
ranges of 5 to 15% by mass, 5 to 10% by mass and 1 to 5% by mass,
respectively.
[0033] The silicic compound containing an alkali metal preferably
is in the range of 10 to 100% by mass and more preferably in the
range of 25 to 70% by mass on the basis of silicon dioxide
(SiO.sub.2) with respect to the mass of cellulose contained in the
undiluted viscose solution. Since the silicic compound containing
an alkali metal in the viscose solution is considered to react with
the sulfuric acid (H.sub.2SO.sub.4) and turn into silicon dioxide
(SiO.sub.2; in the form of polymer), the values are expressed on
the basis of silicon dioxide (SiO.sub.2). The silicon dioxide
contained in the mentioned range makes it possible to maintain the
strength and texture of the fiber, so that, when treated with the
sodium-containing solution, a rayon fiber having favorable
flameproofness can be manufactured.
[0034] The silicate compound containing an alkali metal can be, for
example, sodium silicate. The process of adding the silicate
compound containing an alkali metal such as sodium silicate may be
carried out by mixing an aqueous solution of the silicate compound
containing an alkali metal in a general undiluted viscose
solution.
[0035] The ratio of the sodium silicate to be added is preferably
in the range of 10 to 100% by mass, more preferably in the range of
15 to 80% by mass and particularly preferably in the range of 30 to
70% by mass on the basis of SiO.sub.2 with respect to cellulose in
the undiluted viscose solution. By setting the amount of sodium
silicate to the mentioned range, it is possible to adjust the
amount of silicon dioxide contained in the fiber to be treated to
the amount suitable for the flameproof rayon fiber according to the
present invention. For the sodium silicate, sodium silicate No. 3
(JIS K 1408) can be used, for example.
[0036] Also, in the scouring or aftertreatment process, the fiber
to be treated containing a silicon component that has been obtained
in the spinning process is treated with the solution having a pH in
the range of 4 to 11 and a buffer action and containing sodium,
thereby allowing the silicon and the sodium to react with each
other, so that a compound containing silicon and sodium is formed.
The compound containing silicon and sodium is estimated to form
sodium silicate. For example, there are a treatment of bringing the
fiber to be treated into contact with the sodium-containing
solution having a buffer action in place of sulfuric acid after
bleaching during the scouring process; a treatment of bringing the
fiber to be treated into contact with the sodium-containing
solution having a buffer action after souring during the scouring
process; a treatment of mixing an oil solution component with the
sodium-containing solution having a buffer action and brining the
fiber to be treated into contact with the mixed solution in an oil
solution treatment in the scouring process; and a treatment of
steeping the fiber to be treated in the sodium-containing solution
having a buffer action (as an aftertreatment process) after
scouring and drying the fiber to be treated. At this time, the bath
ratio may be selected suitably in accordance with the
sodium-containing solution having a buffer action to be used, and
the mass of the fiber to be treated the mass of the solution is in
the range of 1:10 to 1:1000, for example. Further, it is generally
possible to carry out favorable treatment when the bath temperature
is in the range of 0 to 100.degree. C. and the steeping time is
about 30 sec, and preferably in the range of 20 to 300 sec.
[0037] The sodium-containing solution having a buffer action may
have a pH in the range of 4 to 11, preferably in the range of 6 to
10, more preferably in the range of 7 to 8.6, and particularly
preferably in the range of 7.3 to 8.6. When the pH is less than 4,
sodium does not penetrate the fiber, so that self extinguishability
cannot be achieved. On the other hand, when the pH exceeds 11, the
silicic acid content in the fiber leaches out, resulting in a low
ash content after the treatment. Consequently, it becomes difficult
to achieve the flameproofness.
[0038] Further, in terms of bringing sodium into reaction with
silicic acid in the fiber in an efficient manner, the
sodium-containing solution having a buffer action is preferably an
aqueous solution having a pH in the range of 4 to 11. In the
present invention, the "sodium-containing solution having a buffer
action" refers to a solution having a buffer action, in other
words, a buffer solution containing sodium and having a pH in the
range of 4 to 11 and the solution may in any form. For example, it
is possible to use a buffer solution containing water-soluble
sodium salt having no buffer action and sodium salt having a buffer
action, a buffer solution containing sodium salt having a buffer
action, and a buffer solution containing water-soluble sodium salt
having no buffer action and an agent having a buffer action such as
weak acid or weak base. In particular, a buffer solution containing
sodium salt having a buffer action is preferable in terms of taking
sodium into the fiber in an efficient manner. As the water-soluble
sodium salt having no buffer action, sodium chloride, sodium
sulfate, sodium nitrate or the like can be used. Examples of sodium
salts having a buffer action include sodium hydrogen carbonate
(baking soda), sodium carbonate, disodium hydrogen phosphate,
sodium dihydrogen phosphate, and sodium citrate. In particular, a
buffer solution of alkalescent sodium carbonate or sodium hydrogen
carbonate is more preferable in terms of applications where
inclusion of phosphorus components is undesirable or in terms of
pH. Further, these sodium salts can be used in combination of two
or more.
[0039] The sodium salt content of the sodium-containing solution
having a buffer action is preferably defined by the concentration
of sodium ions in terms of controlling the solution. The
concentration of sodium ions in the sodium-containing solution
having a buffer action is preferably in the range of 500 to 10,000
mg/L, and more preferably in the range of 1,000 to 8,000 mg/L.
[0040] As a result of the inclusion of the flameproof rayon fiber,
a flameproof fiber structure such as woven fabric, knit fabric and
nonwoven fabric can be obtained. The content of the flameproof
rayon fiber in the flameproof fiber structure is preferably 30% by
mass, and more preferably 60 to 80% by mass. When the content of
the flameproof rayon fiber is 30% by mass or more, it is possible
to obtain a flameproof fiber structure having excellent
flameproofness and flame retardance. Other fibers used in the
flameproof fiber structure are not particularly limited, and
examples of the other fibers include binder fibers such as
low-melting polyester fibers, flame retardant acrylic (modacrylic)
fibers such as "Kanekaron" (trade name, manufactured by Kaneka
Corporation) and nonflammable fibers such as aramid (aromatic
polyimide) fibers.
[0041] As described above, the flameproof rayon fiber according to
the present invention is a rayon fiber having favorable
flameproofness and flame retardance. Further, the rayon fiber has
excellent texture, resistance to dry-cleaning and biodegradability.
The flameproof rayon fiber according to the present invention is
processed into woven fabric, knit fabric, nonwoven fabric, etc. and
useful for the purposes such as disaster prevention items, kitchen
fan filters, sheets, pillow cases, bedding mats, bedding covers,
fire protection screens, interior goods (carpets, chair coverings,
curtains, wall paper bases, wall materials, etc.), vehicle interior
materials (mats, lining fabric, etc.), etc., for example.
EXAMPLES
[0042] Hereinafter, the present invention will be described more
specifically by way of Examples. It should be noted that the
present invention is not limited to the following Examples.
Example 1
(1) Manufacture of Viscose Solution
[0043] An undiluted viscose solution containing 8.5% by mass of
cellulose, 5.7% by mass of sodium hydroxide and 2.6% by mass of
carbon disulfide was produced. Then, a mixture solution of No. 3
sodium silicate, sodium hydroxide and water was added to the
produced undiluted viscose solution such that cellulose and sodium
hydroxide accounted for 7.2% by mass and 7.4% by mass of the
composition of the viscose solution, respectively, thus making a
sodium silicate-added viscose solution. The ratio of added sodium
silicate was 50% by mass on the basis of SiO.sub.2 with respect to
the mass of cellulose.
(2) Spinning
[0044] The sodium silicate-added viscose solution was spun at a
spinning speed of 50 m/min and at a stretch ratio of 50% by two
bath stretch spinning, thus obtaining fibers having a fineness of
about 3.3 dtex. The composition of a first bath (spinbath) was such
that a sulfuric acid accounted for 115 g/liter, zinc sulfate
accounted for 15 g/liter and sodium sulfate accounted for 350
g/liter, and the temperature of the first bath was 48.degree. C.
and the temperature of a second bath (hot water bath) was set to
85.degree. C. The sodium silicate-added viscose solution was
extruded through a spinneret, thus producing a silicon-containing
rayon filament tow (fibers to be treated).
(3) Scouring
[0045] The filament tow cut into a fiber length of 51 mm with a
cutter was used in the scouring process. The scouring process
included a hot water treatment, bleaching, souring and
water-washing in this order. Excess moisture was removed by
compression rollers, followed by drying for seven hours in a
constant-temperature dryer at 60.degree. C. The resultant fibers to
be treated had physical properties such as a fineness of 3.3 dtex,
a dry strength of 1.4 cN/dtex, a wet strength of 0.8 cN/dtex, a dry
elongation of 25% and a wet elongation of 20%.
(4) Aftertreatment
[0046] As a sodium-containing solution having a buffer action
(hereinafter referred to as a sodium-based buffer solution), an
aqueous solution (bath temperature: 50.degree. C., pH: 7.76)
containing 0.38% by mass of sodium sulfate and 0.05% by mass of
sodium hydrogen carbonate was used. In this aqueous solution, the
dried fibers to be treated were steeped for 30 sec. At this time,
the bath ratio was set such that the mass of the fibers to be
treated:the mass of the aqueous solution was 1:20. Next, the fibers
to be treated were washed with water and then dewatered
centrifugally. Finally, the fibers were dried in a
constant-temperature dryer at 105.degree. C. for 30 minutes, thus
obtaining flameproof rayon fibers b of Example 1 (in the following,
referred to as the fibers b).
Example 2
[0047] Flameproof rayon fibers c (hereinafter referred to as the
fibers c) of Example 2 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 7.79) containing 0.34% by mass of sodium sulfate
and 0.1% by mass of sodium hydrogen carbonate was used as a
sodium-based buffer solution in the aftertreatment.
Example 3
[0048] Flameproof rayon fibers d (hereinafter referred to as the
fibers d) of Example 3 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 7.93) containing 0.17% by mass of sodium sulfate
and 0.3% by mass of sodium hydrogen carbonate was used as a
sodium-based buffer solution in the aftertreatment.
Example 4
[0049] Flameproof rayon fibers e (hereinafter referred to as the
fibers e) of Example 4 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 7.31) containing 0.41% by mass of sodium sulfate
and 0.01% by mass of sodium hydrogen carbonate was used as a
sodium-based buffer solution in the aftertreatment.
Example 5
[0050] Flameproof rayon fibers f (hereinafter referred to as the
fibers f) of Example 5 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.40) containing 0.1% by mass of sodium hydrogen
carbonate was used as a sodium-based buffer solution in the
aftertreatment.
Example 6
[0051] Flameproof rayon fibers g (hereinafter referred to as the
fibers g) of Example 6 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.42) containing 0.5% by mass of sodium hydrogen
carbonate was used as a sodium-based buffer solution in the
aftertreatment.
Example 7
[0052] Flameproof rayon fibers h (hereinafter referred to as the
fibers h) of Example 7 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.43) containing 1.0% by mass of sodium hydrogen
carbonate was used as a sodium-based buffer solution in the
aftertreatment.
Example 8
[0053] Flameproof rayon fibers i (hereinafter referred to as the
fibers i) of Example 8 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 4.69) containing 0.5% by mass of sodium
dihydrogen phosphate was used as a sodium-based buffer solution in
the aftertreatment.
Example 9
[0054] Flameproof rayon fibers j (hereinafter referred to as the
fibers j) of Example 9 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 4.53) containing 1.0% by mass of sodium
dihydrogen phosphate was used as a sodium-based buffer solution in
the aftertreatment.
Example 10
[0055] Flameproof rayon fibers k (hereinafter referred to as the
fibers k) of Example 10 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 4.24) containing 3.0% by mass of sodium
dihydrogen phosphate was used as a sodium-based buffer solution in
the aftertreatment.
Example 11
[0056] Flameproof rayon fibers 1 (hereinafter referred to as the
fibers 1) of Example 11 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 10.86) containing 0.5% by mass of sodium
carbonate was used as a sodium-based buffer solution in the
aftertreatment.
Example 12
[0057] Flameproof rayon fibers m (hereinafter referred to as the
fibers m) of Example 12 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.70) containing 0.5% by mass of disodium
hydrogen phosphate was used as a sodium-based buffer solution in
the aftertreatment.
Example 13
[0058] Flameproof rayon fibers n (hereinafter referred to as the
fibers n) of Example 13 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.76) containing 1.0% by mass of disodium
hydrogen phosphate was used as a sodium-based buffer solution in
the aftertreatment.
Example 14
[0059] Flameproof rayon fibers o (hereinafter referred to as the
fibers o) of Example 14 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.79) containing 3.0% by mass of disodium
hydrogen phosphate was used as a sodium-based buffer solution in
the aftertreatment.
Example 15
[0060] Flameproof rayon fibers p (hereinafter referred to as the
fibers p) of Example 15 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.3) containing 0.2M of disodium hydrogen
phosphate and 0.2M of sodium dihydrogen phosphate at a ratio
(volume ratio) of 94.7:5.3 was used as a sodium-based buffer
solution in the aftertreatment.
Example 16
[0061] Flameproof rayon fibers q (hereinafter referred to as the
fibers q) of Example 16 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 8.0) containing 0.2M of disodium hydrogen
phosphate and 0.2M of sodium dihydrogen phosphate at a ratio
(volume ratio) of 91.5:8.5 was used as a sodium-based buffer
solution in the aftertreatment.
Example 17
[0062] Flameproof rayon fibers r (hereinafter referred to as the
fibers r) of Example 17 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 7.6) containing 0.2M of disodium hydrogen
phosphate and 0.2M of sodium dihydrogen phosphate at a ratio
(volume ratio) of 81:19 was used as a sodium-based buffer solution
in the aftertreatment.
Example 18
[0063] Flameproof rayon fibers s (hereinafter referred to as the
fibers s) of Example 18 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 7.2) containing 0.2M of disodium hydrogen
phosphate and 0.2M of sodium dihydrogen phosphate at a ratio
(volume ratio) of 61:39 was used as a sodium-based buffer solution
in the aftertreatment.
Example 19
[0064] Flameproof rayon fibers t (hereinafter referred to as the
fibers t) of Example 19 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 6.8) containing 0.2M of disodium hydrogen
phosphate and 0.2M of sodium dihydrogen phosphate at a ratio
(volume ratio) of 37.5:62.5 was used as a sodium-based buffer
solution in the aftertreatment.
Example 20
[0065] Flameproof rayon fibers u (hereinafter referred to as the
fibers u) of Example 20 were manufactured in the same manner as
Example 1 except that an aqueous solution (bath temperature:
50.degree. C., pH: 6.3) containing 0.2M of disodium hydrogen
phosphate and 0.2M of sodium dihydrogen phosphate at a ratio
(volume ratio) of 18.5:81.5 was used as a sodium-based buffer
solution in the aftertreatment.
Comparative Example 1
[0066] Flameproof rayon fibers a (hereinafter referred to as the
fibers a) of Comparative Example 1 were manufactured in the same
manner as Example 1 except that the fibers to be treated were not
subjected to aftertreatment with an aqueous solution containing
sodium.
Comparative Example 2
[0067] Commercially available rayon fibers (trade name: "FELON",
manufactured by Shandong Helon Co., LTD, hereinafter simply
referred to as FELON) were used as Comparative Example 2.
Comparative Example 3
[0068] Flameproof rayon fibers v (hereinafter referred to as the
fibers v) of Comparative Example 3 were manufactured in the same
manner as Example 1 except that an aqueous solution (bath
temperature: 50.degree. C., pH: 7.8) containing 3% by mass of
sodium sulfate was used in the aftertreatment.
[0069] For the flameproof fibers of Examples 1 to 20 and
Comparative Examples 1 to 3, a performance test was conducted as
follows. Tables 1 and 2 provide the results of the performance
test.
[0070] (Performance Test)
(1) Ash Content
[0071] The ash content was measured in conformity with JIS L 1015
8.20. Specifically, the mass of a component remaining after burning
each of the fibers having a mass of 1 g for two hours in an
electric furnace at 850.degree. C. was measured so as to determine
the ash content of each of the fibers. Incidentally, the ash
content is a percent by mass of the mass of the residual component
after burning with respect to the mass obtained by subtracting a
water content from the mass of the fibers. Further, after the
fibers were washed with water, their ash contents were determined
in the same manner. The water-washing was carried out as
follows.
[0072] [Water-Washing]
[0073] To the water-washing, a water absorption test method (weaved
basket method) as one of the purity test methods for absorbent
cotton defined by the Japanese Pharmacopoeia was applied.
Specifically, 2 g of fibers were scaled and they were put into a
container. As the container, a cylindrical basket processed with an
enameled wire and having a height of 8 cm and a diameter of about 5
cm.phi. was used. After putting the fibers into the container
uniformly, the container was steeped in ion-exchanged water at
25.degree. C. for three minutes. Subsequently, the fibers were
taken out from the container and dewatered centrifugally, followed
by drying in a drier. The dried fibers were used as a water-washed
sample.
(2) Flame Retardance
[0074] The fibers were spread flat into a plate shape, subjected
directly to a flame of a disposable lighter (the flame length: 2.5
cm) that was located 2 cm below them, and observed. The flame was
applied perpendicularly to the fiber mass. It is noted that each
evaluation sample (fiber mass) was produced by opening 1 to 2 g of
cut fibers into a web using a carding machine and rendering this
web in the form of fiber mass. Further, the fibers were
water-washed in the manner described above, subjected to a flame in
the same manner and observed. On the basis of the observation
results, the flame retardance was evaluated on a scale from A to D
as follows.
A: when a flame was brought close to a fiber mass, only the part to
which the flame was applied burned and the remaining part did not
burn. B: when a flame was brought close to a fiber mass, fire
traveled somewhat on the surface of the fiber mass but went out
when the flame was moved away. C: when a flame was brought close to
a fiber mass, fire traveled on the surface of the fiber mass and
the fire remained even when the flame was moved away. D: when the
flame was brought close to a fiber mass, fire spread.
[0075] In the above, general rayon fibers were evaluated as D as a
result of observing them. They were manufactured by a general
manufacturing method where sodium silicate was not added to viscose
and aftertreatment with an aqueous solution containing sodium was
not performed.
[0076] (Whiteness)
[0077] The whiteness (L value) was measured in conformity with JIS
L 1015 8.17 C (by Hunter) as follows. 20 g of fibers opened with a
carding machine were placed in a constant-temperature ventilation
drier (trade name: "FC-612", manufactured by Advantec Toyo Kaisha,
Ltd.) set at a temperature of 190.degree. C. for heat treatment for
five minutes, thus producing a sample. A whiteness meter "ZE-2000"
manufactured by Nippon Denshoku Industries Co., LTD. was used to
measure the whiteness. 20 g of the produced sample was put into a
container included with the whiteness meter and the orientation of
the sample was changed to measure the color four times (L, a, b).
The average of the values (L values) obtained from the four
measurements was adopted as the fiber whiteness.
[0078] (Measurement of LOI)
[0079] In conformity with JIS L 1091 E (oxygen index test) and with
the use of an oxygen index flammability tester (ON-1 type)
manufactured by Toyo Rika Kogyo Co., LTD, a twisted fiber string
(E-1) or nonwoven fabric (E-2) as a test piece was attached to a
holder to measure the LOI value. The test piece was produced as
follows.
[0080] E-1 test piece (twisted fiber string): 1 g of a sample
staple was opened and adjusted to have a fiber length of 20 to 30
cm. Then, the fibers were fixed on one end and twists were applied
to the fibers from the other end. Specifically, twists were applied
to the fibers while pulling the fibers, and the application of
twists was stopped immediately before the emergence of bumps.
Subsequently, the twisted fibers were folded into two parts at the
center, thus producing a twisted fiber string having a length of
about 110 mm and a width of about 6 mm.
[0081] E-2 test piece (nonwoven fabric): 30% by mass of low-melting
polyester fibers (trade name: "4080", manufactured by Unitika LTD.,
fineness: 4.4 dtex, fiber length: 51 mm) and 70% by mass of the
flameproof rayon fibers were mixed with each other, the mixture was
rendered in the form of card webs using a carding machine, and the
card web was placed on another such that the total mass per unit
area reached 300 g/m.sup.2. Subsequently, the card web were placed
on a punching plate, a nylon mesh was placed on top of the card
webs, and a weight was placed on top of the nylon mesh such that a
load of 20 g/cm.sup.2 was applied thereto. Then, they were placed
in a constant-temperature ventilation drier (trade name: "FC-612",
manufactured by Advantec Toyo Kaisha, Ltd.) set at a temperature of
180.degree. C. After being set aside for 10 minutes in the drier,
they were taken out and thus obtaining a nonwoven fabric having a
length of 150 mm and a width of 60 mm.
[0082] (Ashing)
[0083] The fibers were set aside in an electric furnace set to a
default temperature of 800.degree. C. and ashing of the fibers was
observed with a microscope (trade name: "ECLIPSE E600",
manufactured by Nikon Corporation, magnification: 320.times.) to
check the presence or absence of softening and the presence or
absence of bubbles.
TABLE-US-00001 TABLE 1 After after- After water- Aqueous solution
(bath) used treatment washing in aftertreatment Flame Flame
Concentra- Concentra- Ash retard- Ash retard- tion of each tion of
content ance content ance Composi- composition Na.sup.+ (% by
evalua- (% by evalua- Whitness Ashing tion (% by mass) pH (mg/L)
mass) tion mass) tion (L value) (800.degree. C.) Comp. 1 fibers a
(untreated) -- -- -- 29.5 C 29.2 C 88.05 not softened EX. no
bubbles 2 HELON -- -- -- -- 31.2 B to C -- -- 74.18 not softened no
bubbles 3 fibers v Na.sub.2SO.sub.4 1.0 7.9 3239 31.0 C -- C -- not
softened no bubbles Ex. 1 fibers b Na.sub.2SO.sub.4/ 0.38/0.05 7.76
1368 29.2 A 29.2 A to B 68.07 partially softened NaHCO.sub.3
bubbles partially present 2 fibers c Na.sub.2SO.sub.4/ 0.34/0.10
7.79 1375 29.5 A 29.5 A to B 67.85 softened NaHCO.sub.3 small
surface asperities bubbles present 3 fibers d Na.sub.2SO.sub.4/
0.17/0.3 7.93 1372 29.6 A 29.1 A to B 54.38 partially softened
NaHCO.sub.3 bubbles present 4 fibers e Na.sub.2SO.sub.4/ 0.41/0.01
7.31 1356 30.0 B 29.5 B 78.69 softened NaHCO.sub.3 surface
asperities present bubbles partially present 5 fibers f NaHCO.sub.3
0.1 8.40 274 29.4 B 28.8 B 76.08 softened surface asperities
present bubbles present 6 fibers g NaHCO.sub.3 0.5 8.42 1369 30.9 A
28.7 A to B 58.06 partially softened no bubbles 7 fibers h
NaHCO.sub.3 1.0 8.43 2737 38.2 A 33.0 A 48.30 softened large
surface asperities bubbles present 8 fiber i NaH.sub.2PO.sub.4 0.5
4.69 958 30.0 B -- -- 83.74 partially softened bubbles present 9
fibers j NaH.sub.2PO.sub.4 1.0 4.53 1916 29.4 B -- -- 81.39
softened small surface asperities bubbles present 10 fibers k
NaH.sub.2PO.sub.4 3.0 4.24 5748 30.7 B -- -- 85.35 partially
softened bubbles partially present 11 fibers l Na.sub.2CO.sub.3 0.5
10.86 2170 40.3 A -- -- 39.70 partially softened bubbles present 12
fibers m Na.sub.2HPO.sub.4 0.5 8.70 1620 29.4 A -- -- 55.33
partially softened no bubbles 13 fibers n Na.sub.2HPO.sub.4 1.0
8.76 3239 29.9 A -- -- 60.26 softened small surface asperities
minute bubbles present 14 fibers o Na.sub.2HPO.sub.4 3.0 8.79 9717
35.6 A -- -- 47.41 partially softened no bubbles 15 fibers p
Na.sub.2HPO.sub.4/ 2.69/0.13 8.30 4476 31.3 A -- -- -- partially
softened NaH.sub.2PO.sub.4 bubbles present 16 fibers q
Na.sub.2HPO.sub.4/ 2.60/0.20 8.00 4402 32.2 A -- -- -- partially
softened NaH.sub.2PO.sub.4 bubbles present 17 fibers r
Na.sub.2HPO.sub.4/ 2.30/0.46 7.60 4161 30.9 A -- -- -- partially
softened NaH.sub.2PO.sub.4 bubbles present 18 fibers s
Na.sub.2HPO.sub.4/ 1.73/0.94 7.20 3702 31.1 A -- -- -- partially
softened NaH.sub.2PO.sub.4 bubbles present 19 fibers t
Na.sub.2HPO.sub.4/ 1.07/1.50 6.80 3161 30.5 A to B -- -- --
partially softened NaH.sub.2PO.sub.4 no bubbles 20 fibers u
Na.sub.2HPO.sub.4/ 0.53/1.96 6.30 2725 31.0 B -- -- -- partially
softened NaH.sub.2PO.sub.4 no bubbles
TABLE-US-00002 TABLE 2 LOI value Twisted fiber string Nonwoven
fabric (E-1 method) (E-2 method) Ex. fibers b 32.0 24.2 fibers g
32.9 25.4 fibers l 38.2 30.2 fibers m 33.3 24.8 Comp. fibers a 29.8
18.0 Ex. HELON 30.3 18.8
[0084] As can be seen from Tables 1 and 2, the flameproof rayon
fibers of Examples had an LOI value of 31 or more when measured in
the form of a twisted fiber string (E-1 method) and an LOI value of
24 or more when measured in the form of a nonwoven fabric (E-2
method). Thus, they had excellent flame retardance.
[0085] FIGS. 1 to 4 are micrographs respectively showing the
flameproof rayon fibers of Examples 2 and 5 and Comparative
Examples 1 and 2 being ashed at 800.degree. C. As can be seen from
FIGS. 1 to 4 and Table 1, the fibers of Comparative Examples were
not softened at 800.degree. C. and no bubbles were observed. On the
other hand, the fibers of Examples softened and bubbles were
observed. That is, the fibers of Examples formed a soda glass
structure when being burned, so that their softening point dropped.
Thus, the glass softened quickly in high temperatures and inhibited
the decomposition of cellulose.
[0086] Further, among the fibers b to u (Examples), the fibers e
tended to have somewhat low flame retardance because the component
having a buffer action of the aqueous solution used in the
aftertreatment was in small amount. Further, the fibers f tended to
have somewhat low flame retardance because the concentration of
sodium ions in the aqueous solution used in the aftertreatment was
small. The fibers i, j and k tended to have somewhat low flame
retardance because the aqueous solutions used in the aftertreatment
all had a low pH. On the other hand, the fiber v (Comparative
Example) did not have flame retardance because the aqueous solution
used in the aftertreatment contained sodium but did not contain an
agent having a buffer action, in other words, the aqueous solution
was not a buffer solution containing sodium. It is considered that
this was due to the absence of sodium in the fibers.
[0087] For the fibers b to h (Examples) and the fibers a and v
(Comparative Examples), their flame retardance after water-washing
was measured. For the fibers b to h, there were substantially no
decrease in the ash content after water-washing and substantially
no change in the flame retardance. Thus, it is considered that
sodium was present in the flameproof rayon fibers of Examples.
[0088] Further, for the fibers b to o (Examples) and the fibers a
and HELON (Comparative Examples), the whiteness of their samples
after heat treatment at 190.degree. C. was measured. The fibers i,
j and k had high whiteness, in other words, they maintained
whiteness but tended to have somewhat low flame retardance. The
fibers l had low whiteness, in other words, they were tinted but
had high flame retardance. The fibers l were at a level that might
result in reduction in product value depending on the applications.
The remaining fibers of Examples all maintained high flame
retardance and product value.
[0089] (Component Analysis)
[0090] The components of the fibers a and HEWN (Comparative
Example) and the fibers b, f and g and the water-washed fibers g
were determined by an X-ray fluorescence analysis as follows. Table
3 provides the results.
[0091] [X-Ray Fluorescence Analysis]
[0092] The X-ray fluorescence analysis was performed using an X-ray
fluorescence spectrometer "LAB CENTER XRF-1700," manufactured by
Shimadzu Corporation, by a theoretical calculation by an FP method.
The outline of this measurement device and the measurement
conditions are as follows.
(i) Outline of the Measurement Device
[0093] Range of elements to be measured: .sub.4Be to .sub.92U
[0094] X-ray tube: 4 kw thin window, Rh target
[0095] Spectral element: LiF, PET, Ge, TAP, SX
[0096] Primary X-ray filter: four-kind automatic exchange (Al, Ti,
Ni, Zr)
[0097] Field stop: five-kind automatic exchange (diameters of 1, 3,
10, 20, 30 mm.phi.)
[0098] Detector: scintillation counter (heavy element),
proportional counter (light element)
(ii) Measurement Conditions
[0099] Tube voltage--tube current: 40 kw-95 mA
[0100] For the measurement, cut fibers of the fibers a and HELON
(Comparative Examples) and the fibers b, f, g and the water-washed
fibers g (Examples) were used. The measurement was made such that
the irradiation surface was adjusted to be 10 mm.phi. in diameter
and several millimeters in thickness and irradiated with light
reaching from above and passing therethrough.
TABLE-US-00003 TABLE 3 Element content (% by mass) Mass ratio O C
Si Na of Si/Na Blank (theoretical value) 57 43 <0.1 <0.1 --
Ex. fibers b 43 39 17.298 0.25 69.2 fibers f 43 41 16.085 0.125
128.7 fibers g 44 40 16.134 0.262 61.6 fibers g (after 44 40 15.553
0.139 111.9 water-washing) Comp. fibers a 46 37 17 <0.1 -- Ex.
HELON 45 37 17.721 0.197 90
[0101] From the results provided in Table 3, it can be considered
that the fibers b, f and g and the waterwashed fibers g contained
components of silicon and sodium and the components formed sodium
silicate. The fibers g were waterwashed to check the resistance of
the flame retardance to waterwashing. As can be seen from the
results of the fibers g after waterwashing provided in Table 3, the
fibers maintained a sodium content of 0.1% by mass or more even
after being washed with water. Further, as can be seen from the
results of the fibers g after waterwashing, at least sodium was
partially present in the fibers. Further, in view of the mass ratio
of Si/Na of the fibers b, f, g and the fibers g after waterwashing
(Examples) and HELON (Comparative Example), it is confirmed that
particularly favorable flame retardance can be achieved when the
mass ratio is less than 90.
[0102] (Flameproof Nonwoven Fabric)
[0103] With the use of a sample staple of each of the fibers b, g,
l and m (Examples) and the fibers a and HELON, flameproof nonwoven
fabrics were produced. 30% by mass of low-melting polyester fibers
(trade name: "4080", manufactured by Unitika LTD., fineness: 4.4
dtex, fiber length: 51 mm) and 70% by mass of a sample staple were
mixed with each other, the mixture was rendered in the form of card
webs using a carding machine, and the card web was placed on top of
another such that the total mass per unit area reached 300
g/m.sup.2. Subsequently, the card webs were placed on a punching
plate, a nylon mesh was placed on top of the card webs, and a
weight was placed on top of the nylon mesh such that a load of 20
g/cm.sup.2 was applied thereto. Then, they were placed in a
constant-temperature ventilation drier (trade name: "FC-612",
manufactured by Advantec Toyo Kaisha, Ltd.) set at a temperature of
180.degree. C. They were set aside in the drier for 10 minutes to
let the low-molten polyester fibers melt to bond the fibers to each
other. The nonwoven fabric was taken out from the drier, and thus
obtaining the flameproof nonwoven fabric. The flameproof nonwoven
fabrics respectively containing the fibers b, g, l and m of
Examples exhibited favorable flame retardance.
INDUSTRIAL APPLICABILITY
[0104] As described above, the present invention can provide a
flameproof rayon fiber having favorable flameproofness for
preventing fire as well as flame retardance
(self-extinguishability), and a method for manufacturing the
flameproof rayon fiber. Also, the rayon fiber, which is the
principal component of the present invention, has biodegradability,
while other components mainly are compounds containing silicon and
sodium, so that a flameproof rayon fiber with a reduced load to the
environment can be provided. In particular, the flameproof rayon
fiber according to the present invention can be used as a material
replacing glass fibers, asbestos, aramid fibers, etc., which have
been used conventionally in flameproof products. The flameproof
rayon fiber according to the present invention is processed into
woven fabric, knit fabric, nonwoven fabric, etc. and useful for the
purposes such as disaster prevention items, kitchen fan filters,
sheets, pillow cases, bedding mats, bedding covers, fire protection
screens, interior goods (carpets, chair coverings, curtains, wall
paper bases, wall materials, etc.), vehicle interior materials
(mats, lining fabric, etc.), etc., for example.
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